linux-kernel - Re: [RFC][PATCH] Disable CLONE

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Message-ID: <20090701080106.GA14762@us.ibm.com>
Date:	Wed, 1 Jul 2009 01:01:06 -0700
From:	Sukadev Bhattiprolu <sukadev@...ux.vnet.ibm.com>
To:	Roland McGrath <roland@...hat.com>
Cc:	Oleg Nesterov <oleg@...hat.com>,
	"Eric W. Biederman" <ebiederm@...ssion.com>,
	Oren Laadan <orenl@...columbia.edu>, serue@...ibm.com,
	Alexey Dobriyan <adobriyan@...il.com>,
	Containers <containers@...ts.linux-foundation.org>,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC][PATCH] Disable CLONE_PARENT for init

Roland McGrath [roland@...hat.com] wrote:
| > When global or container-init processes use CLONE_PARENT, they create a
| > multi-rooted process tree. 
| 
| I take this to be the real motivation for your change.
| But you don't mention it in the code comment.

Well, it was - when I started. But my understanding of the comments was that
the constraint could be extended to global init as well for the following
reason.

| 
| > +	 * Swapper process sets the handler for SIGCHLD to SIG_DFL. If init
| > +	 * creates a sibling and the sibling exits, the SIGCHLD is sent to
| > +	 * the swapper (since the swapper's handler for SIGCHLD is SIG_DFL).
| > +	 * But since the swapper does not reap its children, the zombie will
| > +	 * remain forever. So prevent init from using CLONE_PARENT.
| 
| This would be fixed by having swapper set its SIGCHLD to SIG_IGN instead,
| so such children self-reap.  That seems like the better fix for that.

Yes, that would fix the global init case.

| 
| If you want to make this change because of container-init issues, I think
| you should just say so independent of this global-init case.

So can I leave the check for SIGNAL_UNKILLABLE but simplify the comments
to refer to the multi-rooted process tree ?
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